Television image production



Sept., 24, 1946. l G. K. TEAL I 2,403,108

TELEVISION' IMAGE PRODUCTION Filed May'll, 194s 4 sne'ets-sneet 1IMPULSE GENERATOR sept. 24, 19h46. K, TEAL 2,408,108

TELEVISION IMAGE PRODUCTION Filed May l1, 1943 4 Sheets-Sheet'Z SECONDTUBE cer QQ L u /NVENTOR @.K. TEAL er Sept. 24, 1946. G, K, TEALTELEVISION IMAGEv APRODUCTION Filed May 1l, 1945 4 Sheets-Sheet 3,

/NVE/VTOR a/c 7.5MY

Patented Sept. 24, 1946 TELEVISION Ill/[AGE PRODUCTION Gordon K. Teal,Summit, N. J., assignor to Bell Telephone Laboratories, Incorporated,New York, N. Y., a corporation of New York Application May 11, 1943,Serial No. 486,533

Claims. 1

This invention relates to electric signaling and particularly to amethod of and apparatus for Vproducing television images of a field ofView at a rate higher than that of scanning the field of view.

In accordance with an embodiment of the invention herein shown anddescribed for the purpose of illustration, there are provided at atelevision receiving station a plurality of cathode rayrecorder-transmitter tubes each for alternately non-pictoriallyrecording an image and controlling the production of the image from therecord. Each recording of an image takes place in a period equal to aframe scanning period of the image signal generated at a televisiontransmitting station, that is, the period required for scanning theentire eld of view. The recordings are scanned in succession to produceelectric signaling energy which is impressed upon an image producingdevice for controlling the production of television images, eachrecording being completely scanned and each television image beingproduced in a period less than the frame scanning period ofthe field ofview so that the television images are produced at a frame frequencyhigher than the frame frequency of the scanning of the field of view andof the resulting television signal. If T represents the frame scanningperiod at the transmitter, t the frame scanning period of the imageproduction at the receiver and n the number of recorder-transmitterdevices, then If, for example, 1A5 second is required for comand a thirdrecorder-transmitter will transmit tov the image producing apparatus,vduring the rst half of the frame scanning period, an image signal fromthe record which was completed during the preceding frame scanningperiodand will record, during the last halfof the frame vscanning period, .therecording of an image being completed during the following framescanning period. There 4both for the recording and for the generationofvthe image signal.

will thus be produced television images having a frequency of repetitionequal `to twice the frame frequency of the image signal. Similarly ifthe frame frequency of the image signal is 1A.; second and fiverecorder-transmitter tubes are used, images will-be produced at .therate of per second.

In accordance with a feature of the invention there is employedalternately for recording an image and for producing an imageelectromotive force from the record a cathode ray device having a mosaicelectrode one side of which is scanned by a beam of electrons which,during the image recording, impinge upon the mosaic with a velocity.such as to cause the emissionof a larger number of secondary electronsthan the number of primary electrons which impinge thereon and which,during the generation of the image electromotive force, impinge upon themosaic with a velocity such that the ynumber of secondary electronsemitted therefrom is less than the number oi primaryelectrons impingingupon the mosaic surface, the beam being modulated with respect to.intensity during the recording period and having a constant densityduring the period of -generation of the fimage electromotive force.

tained at a beam velocity below the velocity required formaximumsecondaryemission and also at a beam velocity above the velocityrequired for the maximum secondary emission and either the high or theloW velocity beam may -be employed for the generation 4of the imageelectromotive fforce which is to be used at the receiver for controllingthe image production. However, magnetic focussing of the electron beamlis required when a low velocity beam is used to vprevent spreading ofthe beam at the mosaic and,

to avoid the necessity of using a focussing-coil, it is desirable toemploy -a high velocity beam The use of a beam having a very highvelocity makes necessary the use vof accelerating voltagesand deflectingfields of `,high magnitude. It is therefore desirable to employ asecondary emitter mosaic having va secondary emission coeiiicient whichhas a high maximum vaine and which decreases rapidly from its maxi- .mumvalue to a Avalue below `one as the velocity of the bombarding electronbeam is increased.

3 A mosaic electrode having this desirable characteristic comprises adiscontinuous layer of secondary emitter material upon one side of adielectric and a signal plate of electrical conducting material on theother side of the dielectric, the secondary emitter material beingpreferably a caesium carbon alloy or a lm. of magnesium oxide on carbon.Such a mosaic has a secondary emission coefficient less than one whenthe velocity of the electron beam bombarding the mosaic is suiiicientlyhigh to penetrate through the caesium carbon alloy or magnesium oxide tothe carbon which has a secondary emission coecient less than one.

The invention will now be described in detail withreference to theaccompanying drawings in which: Y

Figs. 1, 2 and 3, with Fig. 1 placed above Fig. 2, and Fig. 3 placedbelow Fig. 2, are a diagrammatic View of a complete television systemembodying the invention;

' Fig. 4 is a diagrammatic View of a modification of a portion of thetelevision system shown in Figs. l, 2 and 3; and

Figs. 5 to 8 are diagrams to which'reference will be made in describingythe operation of the television system shown in the preceding gures.

Referring to Figs. l, 2 and 3, there is disclosed a television systemcomprising a transmitter I9 of any well-known type for generating aVcarrier current modulated in accordance with a video signal produced asthe result of scanning a iield of View and having horizontalsynchronizing impulses produced during intervals between successivescanning lines and vertical synchronizing impulses produced duringintervals between successive scannings of the field of View, that is, atthe end of each field and frame scanning period.

The generator of the vertical and horizontal synchronizing impulses usedin the transmitter I0 is connected to the (iO-cycle power source 9 formaintaining the generation of the impulses in synchronism with theV60-cycle power source, as is well known. This current is transmittedover a coaxial conductor cable II or other suitable transmission mediumto a receiving station for controlling the production of images or" thefield of View scanned at the transmitter upon the iiuorescent screen ofa cathode ray image producing tube i2, for example. Apparatus comprisinga plurality of recorder-transmitter cathoderay tubes, each like tube I3of Fig. 1,'is providedv for causing images to be produced upon thescreen of cathode ray tube I2 in'succession at a rate higher than therate of repetition of scanning of the iield of View at the transmitter.Assuming for the present that interlaced scanning is not used and thatthe scanning rate at thetransmitter is 30 framesper second, then theimages of the field of View will be produced at a rate which is anintegral multiple of 30, say 60 frames per second.

4tal impulses being impressed upon a horizontal sweep circuit I'I andthe vertical synchronizing impulses being impressed upon a verticalsweep circuit I8 in well-lmown manner. The saw- -toothed wave generatedin the horizontal sweep circuit is impressed upon the conductors I9 andthe saw-toothed wave generated in the vertical sweep circuit isimpressed upon the conductors 25.

The cathode ray beam of the image producing tube I2, like the scanningbeam used in the television transmitter I0, is deflected in synchronismwith the 60-cycle power source 9 to which the synchronizing impulsegenerator 2l is connected. The vertical and horizontal scanning impulsesderived from the generator 2I are supplied to the vertical andhorizontal sweep circuits 22 and 23, respectively, the output circuitsof which are connected to the lines 24 and 25, respectively, the outputof the vertical sweep circuit 22 being connected through an amplier IISto the vertical deecting coils, not shown, of the cathode ray tube I2and the output of the horizontal sweep circuit 23 being connectedthrough an amplifier l II to the horizontal deflecting coils of thecathode ray tube I2.

The cathode ray recorder-transmitter tube I3 comprises an evacuatedchamber or bulb having therein an indirectly heated cathode for emittingelectrons, a modulating or control electrode 3i, accelerating anodes 32and 33, a collector anode 45 and a mosaic electrode upon which thecathode ray beam impinges. The mosaic electrode comprises a sheet ofdielectric material 34, glass, for example, a secondary electronemitting surface and a signal plate 36 of a conducting material such asplatinum or aluminum. The surface 35 is formed by insulating silveroxide upon the dielectric sheet 34, reducing the oxide to silver, thenoxidizing the silver and treating the surface with caesium or othersecondary electron emitting material.

One terminal of an output resistor 31 is connected to the conductingplate 36 of the mosaic 4oelectrode, the other terminal being connectedto ground.A The positive terminal of battery 38 is connected to thecollecting cylinder 40, the negative battery terminal being grounded.Accelerating potentials from a'potentiometer 4I which is connectedacross battery 38 are applied through contacts of cam switch d to theelectrodes 32 and 33. The electron beam is focussed upon the mosaicelectrode due to the electromagnetic eld set up by the winding 42 whichis energized by direct current from battery 43 through a circuitincluding a variable resistor 44. The electron beam is deiiected by theelectromagnetic field which is set up due to the energization of thevertical deflecting coils 45 and the horizontal deflecting coils 45. Theoutput circuit of video arnplier I5 is connected across a circuitcomprising battery 4I,`having a potentiometer 48 connected across itsterminals, and a resistor 49 in series with battery 41.

Thereare provided a plurality of recordertransmitter tubes, each liketube I3, together with the associated circuit elements and connectionsas shown within the area deiined by the dashdot line 50 of Fig. l. Thisadditional apparatus is not shown in detail, but, for purpose ofsimplication, is indicated by the dash-dot lines 5I and 52 of Figs. 2and 3, respectively, the area defined by each of these lines including arecordertransmitter tube like tube I3 and the associated circuitelements and connections as shown within the area defined by the line5i) of Fig. l. Video signal voltage from the television receiver I4 issupplied to circuits 5I and 52, respectively,

through line 54 and amplifiers 55 and 56, like ampliiier I5.v

i In each of -the diagrams shown in Figs. 5,V 6 and-7 the abscissa isdivided into periods each Yof 1450 Vsecond duration. Referring briey toFig. 5, it is-indicated that the rst recorder-transmitter tube isin therecording condition during the -first two-periods and inthe-transmitting conudition A'during the third period. The second tubeVrecords during periodstwo and three and trans- Vmits during periodfour. The third tube records Vduring periods three and four andtransmits during period five.

' For the purpose of causing each or" the recorder-transmitter tubeslike I3 alternately to vnon-picto'rially record an image under controlof a received video signal and to transmit from the record forcontrolling the production of an image upon the cathode ray Yimageproducing-tube I2, during time periods as indicated in Fig. 4, forexample, there are provided a plurality of cam switchescomprising camsSila to GEZ, inclusive, and -a commutator switch having a brush arm63,-the cams and brush arm being driven at the rate of 400 revolutionsper minute by means of synchronous motor It, energized from 60-cyclepower source 9, and suitable gearing not shown. The cam 'followers ma tolill, inclusive, for cams 60a to YIiIBZ, respectively, operate the camvswitches 80a to 891, respectively. The commutator has la brush 73 whichrides on the conducting ring 89 and nine conduct-ing segments 9i to 53,inclusive, 'of equal length. As the brush arm rotates a circuit iscompleted from the output resistors 3l, I and IGI in succession to thecontrol circuit of the cathode ray image producing tube 2. For theconditions specifically depicted in Figs. 1, 2 and 3, the switches ta to80h, inclusive, are closed to the right-hand contact as viewed in Figs.1 and 2, and the recorder-transmitter devices 50 and 5| are in therecording condition. At the saine time the switches 302 to 801 areclosed to the left-hand contacts as viewed in Fig. 3 so that therecorder-transmitter 5.2 is in the transmitting condition. It will benoted that any instant during the operation, one of the threerecorder-transmitter devices will be set to transmit while the remainingtwo devices are simultaneously set to record.

The ungrounded side oi amplier i5 is connected `through a circuitcomprising leads |32 and |63 to the control element or modulatingcylinder 3| of the recorder-transmitter tube I3 and the cathode 3B ofthis tube is connected through a circuit comprising leads IM and |95 toa contact on potentiometer 48 which is highly negative with respect toground. Under this condition, the target 3d, 35, 36 cirecorder-transmitter tube I3 is suiciently positive with respect to thecathode to cause the cathode ray beam to irnpinge with a high velocityupon the sensitized surface 35 of the target or mosaic electrode 34, 35,36. Secondary electrons are therefore emitted from the surface 35 of themosaic electrode and each elemental area of the recording mosaic is thuscharged to a potential which is proportional to the instantaneousamplitude of the video signal from amplifier I5. The horizontaldeflecting voltage from the saw-toothed wave generator Il is impressedthrough conductor I9 upon the input circuit of amplifier kIi to producea saw-toothed unidirectional current wave in the amplifier outputcircuit which is connected through switch 80c to horizontal sweep coils63. Similarly the vertical sweep circuit I8 is connected through line20, amplier |01 and switch 83h to vertical Sweep coils-45 to produce asaw-toothed current Wave therein. The cathode ray beam in tube I3 isthus deected in synchronism with the cathode ray beam of the cathode raydevice which scans the field of lview at the transmitter I4. There arethus stored upon the elementalareas of the mosaic electrode 34, 35,3S'charges corresponding to the tone values of the correspondingelemental areas of the eld of view which is being scanned at thetransmitting station.

Assume now that the cams Sila to 3D1 have been rotated sufliciently tobring the apparatus 53,01" Fig. 1 to the transmitting condition and theapparatus 5| and 52 to the recording condition. The cathode 3D is thenconnected through lead It and switch 80a to the grounded negativeterminal of battery IZ and the modulating cyl` inder or controlelectrode 3| is connected through lead |03 and switch 89a to thepositive terminal of battery iii. Under these conditions the mosaicelectrode is at substantially the same potential as the cathode and thecathode ray beam impinging upon the mosaic electrode 34, 35, 33 isunmodulated and has a relatively low velocity such that the ksecondaryemission coefficient of the mosaic electrode is less than unity, thatis, the number of primary electrons reaching the mosaic electrode isgreater than the number of Secondary electrons emitted from theelectrode. Each element of the mosaic surface 35 is thus brought to theequilibrium value of potential, that is, zero volts. The relatively fewsecondary electrons ejected from the mosaic surface and the excesselectrons in the beam are accelerated toward the collec-tor cylinder 4Bwhich is at a high positive potential with respect to the potential ofthe mosaic surface. Saw-toothed Wave deflecting current is applied tothe vertical deiiecting coils l5 from a source 22 through amplifier |38and switch 83h and the horizontal deilecting coils llt are energizedfrom source 23 through amplifier it and switch 89C. Since the verticaland horizontal sweep coils of the image producing tube I2 are energizedat all times from source 22 through amplifier I I0 and from source 23through ampliner I I I, respectively, the mosaic 35 and the screen ofthe image producing tube I2 are scanned in synchronism by the respectivecathode ray beams. As the electron beam scans the mosaic electrode, avideo signal is generated in the resistor 31 and the voltage generatedacross this resistor is impressed upon the modulating electrode of theimage producing tube I2 through a circuit comprising lead II2, one ofcommutator segments 9|, 94 or 91, brush '19, conducting ring 89 and leadI I3 to the cathode ray tube I2. v

Since the mosaic surface is scanned at a higher rate during thetransmitting condition than it is during the recording condition,successive images are produced by the cathode ray tube I2 at a higherrate than the frame scanning rate of the eld of view at the transmitteri8. As mentioned above with reference to Fig. 5, if threerecordertransmitter tubes are used and if the scanning rate at thetransmitter is 30 frames per second, images will be produced by tube I2at the rate of 60 frames per second. If five tubes are used and thescanning rate at the transmitter is l5 frames per second, images will beproduced at the rate of '6G frames per second as depicted in Fig. 7. Theinvention is also of use in a system employing interlaced scanning.Referring to Fig. 6, if the first recorder-transmitter tube records theeven lines of an image during periods one and two and the odd linesduring periods three and four, the even lines ofthe recorded image willbe produced by tube I2 during period iive and the odd lines will beproduced during period'six.l The second tube will-similarly recordduring periods three, four, ve and six and transmit during periods sevenand eight while the third tube will record during periods five, six,seven and veight and transmit during periods nine and ten.

Fig. 4 depicts a modication of the recordertransmitter tube I3 and theassociated circuit arrangement within the dot-dash line I] of Fig. l,the corresponding parts being similarly designated, Thisrecorder-transmitter tube comprises a cathode 39, a modulator electrode3I, accelerating electrodes II4 and I I5, a collector anode All and amosaic electrode. The mosaic electrode comprises a surface IIS ofsecondary emitter material which may be a caesium carbon alloy or a filmof magnesium oxideY on carbon, this secondary emitter material beingdiscontinuous to provide sufficient surface resistance to allow a chargeto be stored on the mosaic. This mosaic surface is supported upon adielectric sheet IVI of titanium oxide, mica, aluminum oxide or quartz.The mosaic electrode is also provided with a metal signal plate II9 ofplatinum or aluminum.

When in the transmitting condition, the negative terminal of battery I2Iis connected through switch 80a to the control electrode SI, thepositive battery terminal being grounded, and a potentiometer |22, whichis connected across battery l2 I, has a variable tap connected to thecathode 30 to make the cathode potential more negative with respect toground than it is during the recording portion of the cycle. ElectrodesI I4 and 40 are connected to the positive side of battery IIB, thenegative side being grounded. Accelerating electrode I l5 is madenegative by connection to potentiometer 4I across battery 38 since, inthis case, the positive terminal of battery 38 is grounded. The positionof the potentiometer connection is controlled through cam switch 82a togive good focus, whatever the potential of the cathode 30 may be at themoment.

The recorder-transmitter tube of Fig. 4 employs a high velocity scanningbeam during both the recording and transmitting periods of its operationand it is therefore not necessary to employ a magnetic iield forfocussing the electron beam.

Curve A of Fig. 8 shows the relationship between the fbombardingpotential of the cathode ray beam on the mosaic electrode and thesecondary emission coefficient for the recordertransmitter tube of Fig.l, while curve B shows this relationship for the recorder-transmittertube of Fig. 4. It is important that the beam current shall never becomesufficiently great to charge an element of the mosaic to a potentialgreater than that for which the secondary emission coefficient isgreater than unity. If this rule is not observed the surface of themosaic tends to become positive relative to the collector cylinder andit no longer will be possible for the secondary electrons ejected fromthe mosaic electrode to be accelerated toward the collector cylinder. Itis `preferable that the maximum value of the beam current should besufiiciently low that the value of secondary emission coeiiicient is notgreatly changed during the recording operation. Referring to curve A,the electron beam impinging on the mosaic has a bombarding potential V3during the recording cycle and this bombarding potential is reducedduring the transmitting cycle to a value between O and V1 such unity. Inthe case of curve B the bombarding potential is V2 during the recordingoperation and it is subsequently increased to a value above' V4 duringthe transmitting operation so that the secondary emission coefficientWill be less than unity. The rapid decrease in secondary emissioncoeicient of the tube of Fig. 4 when the bombarding potential isincreased from V2 to V4 may be explained by the fact that the carbon ofthe mosaic electrode always has a secondary emission coeiicient lessthan unity and therefore the secondary emission coefficient Imust fallto a value below unity when the bombarding potential is increasedsufficiently for the electrons to penetrate the caesium carbon alloy orthe magnesium oxide with which the carbon is coated.

In addition to recording and retransmitting television signals, therecorder-transmitter devices disclosed obviously may be used forrecording and retransmitting other signals, telephone or telegraphsignals, for example, in a system of time division multiplex telephonyor telegraphy. 'The devices may also be used as a means for delayingelectric signals. It is particularly useful when the applied signalshave a wide band of frequency components but may be used with a singlesinusoidal or other pulse. In a broader aspect of the invention scanningof the target may be omitted and the electron emitting material on thetarget may be in the form of a single element rather than a mosaic ofelements.

What is claimed is:

l. In a television system, the combination with means for repeatedlyscanning an object eld in parallel elemental lines to produce an imagecurrent, of three separate beams at a receiving point for makingseparate records of variations of said current and for later reading therecords at twice the speed of recording, and means for causing two ofsaid last-mentioned means to record the same variations during half of afield scanning period While the third means reads a record which waspreviously made by it and for causing said third one of said means torecord and one of the two others to change from recording to reading atthe .beginning of the second half of the field scanning period.

2. In a television system, the combination with means for repeatedlyscanning a ield of View along parallel lines to produce an imagecurrent, the entire eld of View :being scanned in a certain framescanning period, of a plurality of separate means at a receiving pointfor making separate records of variations of said current and for laterreading the records at a speed equal to an integral multiple of therecording speed, and means for causing one of said recording and readingmeans to record during an entire frame scanning period and each of theother of said recording and reading means to record for a portion ofthat frame scanning period and to read a record made by it for theremainder of that frame scanning period, said means being so constructedand arranged that the reading of said records by said diierent recordingand reading means occurs successively.

3. In a television system, the combination with means for repeatedlyscanning a, iield of View along parallel lines to produce an imagecurrent, the entire eld of view being scanned in a certain framescanning period, of a plurality of separate means at a receiving pointfor making separate records of variations of said current and for-laterreading the records at a speed equal to an .integral ,multiple vof therecording speed, and means Vforfcausing one Yof said. recording andreadin'gfmean's to record 'during 'an entire frame scanning period andeach of the other of said recording and reading means to record for aportion of that frame scanning period and to read a record made by itfor the remainder of that frame scanning period said means being 'sdconstructed andarranged that the reading of said records by saiddinerent recording `and reading means occurs successively and that oneof said others of said recording and reading means reads a record whichwas completed by it priorv to the beginning of said frame scanningperiod and the remaining of said others of said recording and readingmeans reads a record which is completed during said frame' scanningperiod.

4. In a television system," the combination with means for repeatedlyscanning a iield of View to produce an image electromotive force, eachscanning of the i'leld 'of View taking place in a certain frame scanningperiod, of n separate recording and reading means each' for alternatelymaking a separate non-pictorial record in a period equal to saidframe'scanning period under control of said `image electromotive forceand for reading the record made by it when completed, said recording andreading means being so constructed and arranged that said records areread in succession `at a rate equal to n-l times the frame scanningrate.

5. The method of recording electric signals and retransmitting signalsfrom the record, comprising the stepsof modulating 'a cathode ray beamfrom a source'of cathode rays under control of a signaling electromotiveforce, utilizing said modulated cathode ray beam to scan a recordingsurfaceto producey a record corresponding to said signalingelectromotive force, interrupting the modulation of the cathode ray beamfrom said source and utilizing the unmodulated cathode ray beam fromsaid source for scanning said recording surface to produce a signalingelectromotive force.

In the method of producing television images under control of atelevision image electromotive force, the steps of modulating a cathoderay beam from a source of cathode rays under control of said televisionimage electromotive force, scanning a recording surf ace with saidmodulated beam to produce a record of an image, interrupting themodulation of the beam from said source and scanning said recordingsurface with said unrno'dulated beam to generate an electromotive forcefor controlling the production of scanning saidfrecording surface Withsaid modplated beam topro'duce'a record of the image, interrupting themodulation of said beam and simultaneously producing a change in theVelocity with which the primary electrons impinge upon said surfacaandscanning said recording surface Withl said unmodulated beam to generatean electromotive force for controlling the production of an image.

r-slnthe methody of Yproducing television imagesunder 4control o'f atelevision image electromotive force, the steps of modulating a cathoderay beam from a source of cathode rays under control of said televisionimage electromotive force, causing the electrons of said beam to impingeupon a recording surface with a certain velocity to cause the emissiontherefrom of a larger numberof' secondary electrons than the number' ofprimary electrons reaching said surface, scanning said recording surfacewith said modulated beam to produce a record ofthe image. interruptingthe modulation of said'beam and simultaneously causing the Velocity withwhich the primary electrons 'of said beam impinge upon said surface toincrease to a value such that the ratio of secondary electrons emittedtothe primary electrons `reaching the surface isl less than unity, andscanning said recording surface vWith said unmodulated :beam ofincreased electron velocity to cause the generation of an electromotiveforce for controlling the production .of an image.

"9. The method of signaling, comprising modulating a cathode ray beamfrom asource of cathode'rays under control of an electromotive forcehaving variations corresponding to signals, causing the electrons ofsaid beam to impinge upona recordingsurface with a certain velocity tocause the emission therefrom of a larger number of secondary electronsthan the number of primaryelectro'ns reaching said surface, interruptingthe modulation of said beam and simultaneously causing the velocity Withwhich the primary 'electrons of said beam impinge upon said surface' toincrease to cause the ratio Vof the secondarx'fv electrons emitted fromsaid surface to the primary electrons'reaching the Vsurfacetobe'reduced'to a value less than unity, and scanning said recordingsurface alternately with said modulated beam at a certain rate toprod'uc'e a record corresponding to said signals and with saidunmodulated beam at an increased rate to generate anelectromotive'force'for con` trolling the reproduction 'of said signals.

10. Cathode ray apparatus for alternately producingunder control ofa'source Vof signaling electror'notive force an electrical recordcorresponding to signals and transmitting from said record to generate asignaling electromotive force, which comprises amosaic electrode havingan electrically conducting signal plate on one lside of a sheet ofdielectric material and a discontinuous surface of 'secondary emittermaterial on the opposite side, said' secondary emitter materialcomprising a first' layer adjacent said di` electric of a materialhaving a secondary emission coeiiicient Which is always less than unityand a second layer on said first of a material which has asecondaryemission coeflicient greaterV than unity when the velocity ofelectrons bombarding the material is within a certain range, means for'scanning said secondary' emitter mosaic With' a signal modulated cathoderay Vbeam having a certain velocity for producing a signal record, andmeans for subsequently scanning the secon'darvl emitter mosaic With anunmodulated cathode ray beam' having a higher velocity such that theprimary electrons penetrate said second layer and reach said: firstlayerk for causing "a sign'al'i'n "il'e'ctromotive force to begenerated. I

lil; Ca't ode' ray apparatus in' accordance with claim '1'0' in whichsaid lrstrla'yer of saidl secondary emitter material is carbon.

12. Cathode ray apparatus in accordance with l1' claim in which said rstlayer of said secondary emitter material is carbon and said lsecond.layer is magnesium oxide.

13. Cathode ray apparatus in accordance with claim 10 in which saidfirst layer of said secondary emitter material is carbon and said secondlayer is an alloy of caesium and carbon.

' 14. A television system-comprising means for scanning a field of Viewline by line at a certain rate to produce a television imageelectromotive force, a'cathode ray recorder-transmitter tube comprisingmeans for producing a cathode ray beam,` means for modulating said beam,a storage electrode having a secondary electron emitting surface, acollector electrode for said secondary electrons and means fordeflecting said cathode ray beam, a cathode ray image producing devicehaving means for Vproducing a cathode ray beam and Vmeans for deflectingsaid beam, means for modulating the cathode ray beam of said1ecorder-transmitter tube, means for causing said modulated beam to scansaid storage electrode in synchronism with the scanning of said iieldof' view to record an image'upon said storage electrode, means forinterrupting the modulation of said cathode ray beam, means forsimultaneously changing the velocity with which the electrons of saidbeam impinge upon said storage electrode, means for causing saidunmodulated beam to scan said storage electrode at a rate greater than arate of scanning said field of view to produce an electromotive forcefor controlling the modulation of the cathode ray beam produced in saidimage producing device, and means for causing the cathode ray beam ofsaid image producing device to scan the image eld in synchronism withthe scanning of said storage electrode by said unmodulated cathode raybeam thereby producing television images at a higher rate than the rateat which said field of View is scanned.

15. A television system comprising means for repeatedly scanning a fieldof view line by line at a certain rate to produce a television imageelectromotive force, a plurality of cathode ray recorder-transmittertubes each comprising a storage electrode, means for producing a cathoderay beam, means for modulating said cathode ray beam, and means fordeecting said cathode ray beam, said storage electrode comprising asecondary electron emitting means and an electrically conducting signalplate separated by a dielectric, means for impressing said televisionimage electromotive force upon the meansffor modulating a plurality ofsaid cathode ray beams simultaneously, means for impressing electricalenergy upon said deecting means to cause a plurality of said cathode raybeams to scan the secondary electron emitting means of a plurality ofsaid storage electrodes in synchronism with the scanning of the field ofview thereby producing simultaneously a plurality of electrical recordscorresponding to the field of View, means for reading said records insuccession to produce an electromotive force for controlling the imageproduction, said means comprising means for interrupting the modulationof said cathode ray beam, and means for simultaneously changing thevelocity of the electrons of said beam, a cathode ray image producingdevice having means for producing an electron beam, means for modulatingsaid beam under control of said lastmentioned electromotive force, andmeans for deflecting said cathode ray beam, and means 12 for energizingthe deecting means of said image producing device and for energizing thedeflecting means of said recorder-transmitter tubes in succession duringthe periods of reading said records respectively to cause said recordsto be read and the corresponding images to be produced in succession ata rate higher than the rate of scanning said field of view.

16. The combination with an electron beam target having a frontconducting layer and a rear conducting layer with a layer of insulationtherebetween, means for generating and directing to said target a beamof electrons which when it reaches said target has successively avelocity within one range and a velocity within a diierent range, saidtwo ranges ,beingI such that the iront conducting layer of said targetVwhich receives the beam has a'secondary electron emitting ratio greaterthan one for one of said ranges and less than one for thev other of saidranges, said beam generating means comprising a cathode and an anode,means for placing said conducting layer ata potential higher than saidanode, and an electrode for collecting electrons emitted from said`front layer whereby when the beam Velocity is within one of said rangesthe potential of said front layer is raised by reason of the largeemission of electrons therefrom and when the beam velocity is within theother of said ranges the potential of said front layer is lowered untilan equilibrium value is reached.

1'7. The combination of claim 16 in which said front layer consists of aplurality of layers oi' different materials respectively and the beamvelocities are such that the one of said lastmentioned layers mostremote from said cathode is reached by said beam only when it has avelocity within the higher of said ranges.

18. The combination of claim 16 in which said front layer comprises alayer of carbon adjacent said layer of insulation and a coating oimaterial on said carbon layer having a higher maximum secondary electronemitting ratio than carbon, the beam velocities being such that the beamreaches said carbon layer only when it has a velocity within the higherof said ranges.

' 19. The method of television image synthesizing which comprisesscanning elemental areas of a field of view in succession at a certainframe of frequency rate to produce an image signal, simultaneouslyproducing two similar recordings with two of a larger number of scanningbeams under the control of said image signal, and subsequently duringthe same frame scanning period continuing the recording with a differentpair of scanning beams.

20. The method of television image synthesizing which comprises scanningelemental areas of a field of view in succession at a certain framefrequency rate to produce an image electromotive forcesimultaneously'modulating a plurality of scanning cathode ray beamsunder control of said image electromotive force, simultaneouslyproducing under control of said cathode ray beams and causing to becompleted in succession at a rate greater than said frame scanning ratea plurality of similar recordings each corresponding to said eld ofview, and producing under control of said recordings in succession asthey are completed television images of said eld of View at a rategreater than said frame scanning rate;

GORDON K. TEAL.

